1. Field of the Invention
The present invention relates to ultrahigh-pressure fluid systems, and in particular, to methods and assemblies for sealing ultrahigh-pressure systems, such as ultrahigh-pressure pumps.
2. Description of the Related Art
High-pressure pumps draw a volume of fluid into the pump on an intake stroke of a plunger, and on a pressure stroke of the plunger, pressurize the volume of fluid to a desired pressure, up to and beyond 87,000 psi. The pressurized fluid flows through a check valve body to an outlet check valve. If the pressure of the fluid is greater than a biasing force provided by high-pressure fluid in an outlet area acting on a downstream end of the outlet check valve, the high-pressure fluid overcomes the biasing force, and passes through the outlet check valve to the outlet area. Typically, a pump has multiple cylinders, and pressurized fluid from the outlet area of each pump is collected in an accumulator. High-pressure fluid collected in this manner is then selectively used to perform a desired function, such as cutting or cleaning. Such pumps are manufactured, for example, by the assignee of the present invention, Flow International Corporation of Kent, Wash.
Applicants believe it would be desirable in many situations to operate such pumps at higher pressures than can be achieved reliably at the present time. For example, when various pump components, such as dynamic seals, are subjected to high pressures, up to and beyond 87,000 psi, the seals have a relatively short fatigue life, failing at undesirably short intervals, causing down time of the machine and lost productivity.
More particularly, as the plunger reciprocates within a bore of the pump cylinder, the plunger passes through a dynamic seal that prevents pressurized fluid in the cylinder from flowing past the plunger into the pump. One such dynamic seal is shown in U.S. Pat. No. 6,086,070 which is incorporated herein by reference in its entirety, and which is assigned to the assignee of the present application, Flow International Corporation. The dynamic seal in U.S. Pat. No. 6,086,070 includes a seal carrier 12 that functions as a backup ring for the seal 18. The seal carrier further includes an annular guidance bearing positioned in an annular groove of the seal carrier, the guidance bearing being axially spaced from the seal. An inner diameter of the seal carrier in the region between the seal and the guidance bearing is larger than an inner diameter of the guidance bearing such that a small gap exists between the seal carrier and the plunger. While such an arrangement operates well at very high pressures, up to and beyond 40,000 psi, the seal tends to extrude through the gap between the seal carrier and plunger when such a dynamic seal is exposed to pressures up to and beyond 87,000 psi.
In yet another currently existing dynamic seal, shown in FIG. 1, a plunger reciprocates through a dynamic seal having a plastic seal, o-ring, and metal hoop seal that are supported by a backup ring made from a bearing material such as aluminum-bronze. The cylinder is tightened along its planar interface with the backup ring by tightening tie rods, as is known in the art. At very high pressures, for example up to and beyond 87,000 psi, the gap between the backup ring and the plunger is not closed uniformly under pressure and again, the seal extrudes through any available gap causing failure of the dynamic seal. Given the very short component life, frequent component replacement is required, resulting in down time of the machine, lost productivity, and possible damage to the pump. Not only are such failures due to extrusion of the seal, but failure may also result from splitting of the plastic seal, and premature o-ring and seal hoop failure caused by relative motion between the high-pressure components.
Therefore, a need exists for an improved dynamic seal that can withstand pressures above 40,000 psi, and more particularly, pressures up to and beyond 87,000 psi. The present invention meets this need.